So, I've installed my MS2, and I'm proceeding with basic tuning, idling, etc.

I finally got it up to temp, and the fan never came on.

The stock ECU has been relieved of all its functions with the exception of controlling the AC, the Alternator, and the Cooling fan.

At the moment it is failing to control any of these things.

Question:

What sensors at minimum still need to be going to the stock ECU to keep it happy enough to still think it is running the motor?


More Info:

I was running with the stock MAP and IAT unhooked. I still have them both installed, but the wires were unhooked and I did not realize until later that I should try with them to see if it makes a difference.

I have the MS2 ECU's fuel pump relay wired to also power up the ASD relay. I was able to jumper out the fan relay, and the fans come on, so I don't think it is a problem with the system power. My MS ECU relay gets power off the ECU power pin, so the ECU is powered up as well (and I have a CEL on). I can scan it, but I know the ECU is pissed in general, so I'm not sure it will help a lot.

One more question:

If this is not something easy to fix, I am considering going full standalone and controlling the fan with the MS ECU. I can run an external regulator for the alternator, so that leaves only the AC.

Am I missing anything? Is the AC easy to run without the 'ac control' stuff that MS3 offers?

Thanks guys.

If you only have the stock ecu to control those three things you might as well just go full standalone then. You can use the voltage regulator to control the alternator and why not just wire the fans to MS since it can control them? As for the AC the stock ecu only controls the ground of the AC relay so the ac relays ground wire would need to be grounded out so the ac will kick on when you push the ac switch.

I guess the Stock ECU also should be running the tach, but I could work that out as well.

I'll have to see what I have left in the way of pins on the MS2 unit.

For AC control, does the condenser fan come on any time the button is pushed? (assuming I ground the AC relay).

I was just planning to leave the stock ECU since it should in theory do a fine job of running those 4 things. This is a budget car for me, not my daily driver nor a show car.

Did you go through mu write up and piggyback the appropriate items? Also, you do still have the stock coolant temp sensor in there and hooked up, correct?

Thanks for the reply.

I did read your guide early on, but it has been a while... reading through it again now.

Why did you need a 4g63 ignitor? I did not understand that... I built my MS2 with BIP373 coil drivers, and I'm running the stock 420 coil. It fires nice it seems, so just curious why you needed it. Maybe logic level spark control w/o bip373s?

For my install, I did have both CLT sensors hooked up, the GM one to the MS ECU and the stock one back to the Factory ECU.

At the time of testing, I did not have IAT or MAP hooked in, because I did not think they were needed (I noticed this at the end of my test session, I was out of time to test with them).

I also notice you tapped TPS to both ECUs? Does the stock ECU need it to run 4 functions I mentioned above? (no fuel or spark anymore)

Next time I get some time to work on it, I'll run my OBDII scanner and sort through the codes for any that might be relevant.

TPS sounds interesting, I'm curious if that being 'out of range' would make it angry, though I'm not at all sure why it would really care.

I did the 4G63 because I did not have internal ignitors. No need for most set-ups.

I wouldn't think that TPS would mean anything to those functions, but you never know, lol. I just wanted to be sure that you piggybacked those inputs (not just cut the wires) to be sure that stock ecu was seeing information.

Funny, I have done a few piggyback set-ups (CT emissions) and haven't had a problem. I find it really curious that you have no alternator. You did piggy back the ignition wire correct?

As in the ignition 12v power to the ECU?

I don't recall the pin number, but I spliced to a cable that went to the ECU... I recall it being like a 10 or 12ga when the others were a bit smaller.

I tapped into it and I use that to run my main 12v relay coil. So, that should be good.

I'm hoping to get back to the project very soon, and I can verify all my sensor functionality.

Luckily I can just run the car and check the alternator voltage until I get the right thing fixed back up. I have a baby, so my days are filled and I can't make that much noise at night... so my time is limited.

Originally posted by Tired2
As in the ignition 12v power to the ECU? I don't recall the pin number, but I spliced to a cable that went to the ECU... I recall it being like a 10 or 12ga when the others were a bit smaller. I tapped into it and I use that to run my main 12v relay coil.

Yeah, you should have piggybacked into a wire that is powered when the key is turned on (I use a black and white wire that is in position B20 off the ECU plug). Sounds like that is what you have done. Can't seem to figure out what you could have done to cut the alternator power. You don't really touch the alternator wires at all. If you piggybacked the ignition wire, then the ECU knows when the ignition is on.

That sounds right. I'll report back when I figure it out.

I've tried a lot of things, and I can't manage to make the stock ecu work anymore.

I can OBDII into it, and all the sensors have good readings. The feedback of the ASD powers JS3 I belive, which powers many of the sensors (MAP for instance), which I have a valid reading for... I've just checked my ASD wiring a few times over, and all seems well.

If I can't work anything else out I'll just have to go stand alone. I was really hoping to keep the stock ECU for those functions, and possibly even keep cruise control. I can't be far off... very frustrating considering the car runs just without fans or battery charging :-/

Any ideas are appreciated.

Bulletdsm, any chance you recall how you did the ASD relay when you wired yours up? I'm about out of ideas, and ready to buy a voltage regulator and wire in fan control to my MS.

Anyone have a part number for a cheap voltage regulator that works on the 420a?

I've once more checked the ASD wiring, and verified even that the alternator has 12v on the red wire, which it does. The field coil wire sits near 0v.

So, I've ordered a voltage regulator.. Tru-Tech VR125T $16 on amazon... sorry symtech. :( Also some relays to run the cooling fan, I'm going full standalone.

I'll be doing videos of the final steps to go full standalone on my youtube channel if anyone who finds this in the future is interested. "Evan's megasquirt build series".

Once you get the standalone running properly you'll be much happier then dealing with all the headaches the stock ecu comes with. To make things a lot simpler you can go with a self exciting alternator so you don't have to worry about wiring in the voltage regulator.I've heard people have problems with voltage regulators

I wired in the vreg last night, new video will be up on my youtube videos tonight or tomorrow.

I was getting 14.8v when running with it, which seemed a tad high, but still fine I think.

Wiring was straight forward. I'll need to do something about the battery light, but I'll probably just unhook it instead of making it work right again, since I plan to have a 7" tablet as a dash board and it will have battery voltage information.

Now I just need the fan relay (I think I'll just reuse my ASD Relay), and I'm good to go. Winter approaches, so I can wait on the AC for a while :)

Just for historical sake... never found out why the ECU was pissed. I went full standalone.

What I never read anywhere though is that you have to power your speed sensor as well with the 5v from megasquirt.